4756 slower than expected

[mmcnx]

I'm loading 45acp and using a hornady 200jfp/xp bullet with IMR 4756

My hornady load manual says 1.23COL and I'm at that or .001 under on the ten cases I hand checked.

I hand weighed each powder throw at 7.8 which is slightly under the 8.1 max the book says.

Trouble is I'm only at 750fps. Not sure but 8.1 in the IMR book says it should be 880. Seems like .3 grains would not make that much of a difference.

I'm using winchester brass and primers.

Even more interesting IMR's online data shows starting load at 7.0 and max at 7.6, with speeds of 842 - 941 respectively.

So at 7.8 I'm either short or over the max according to the two IMR sources, yet my speed is way off.

Chrono checks out KO with other loads that have been chrono'ed on othe units.

Factor WW chrono'ed fine out the same gun.

Any ideas?

Could it be al COL issue, the lenght I'm using is from hornady for the specific bullet. However they don't list my powder, IMR lists a speer 200 jhp bullet with 4756 but an COL of 1.17 which seems very short.

Edited January 30, 2009 by mmcnx

[XRe]

Ideas:

- every gun is different, and yours may not shoot as "fast" as the test barrel that was used

- your bullet may differ somewhat in shape/size from what they tested

- check the length of the test barrel, it may have been longer than yours

- every chrono is different, and theirs may not register as fast as yours

- every scale is different - if you haven't calibrated with check weights, your scale may be off

- 4756 is notoriously variant from batch to batch - they may have worked up loads with a fast batch, and you have a slow batch

4756 in a .45? Hmmm.... Seems like a faster powder might work better for that bullet weight, honestly, at least in terms of recoil and whatnot....

[R.Elliott]

I'm loading 45acp and using a hornady 200jfp/xp bullet with IMR 4756

My hornady load manual says 1.23COL and I'm at that or .001 under on the ten cases I hand checked.

I hand weighed each powder throw at 7.8 which is slightly under the 8.1 max the book says.

Trouble is I'm only at 750fps. Not sure but 8.1 in the IMR book says it should be 880. Seems like .3 grains would not make that much of a difference.

I'm using winchester brass and primers.

Even more interesting IMR's online data shows starting load at 7.0 and max at 7.6, with speeds of 842 - 941 respectively.

So at 7.8 I'm either short or over the max according to the two IMR sources, yet my speed is way off.

Chrono checks out KO with other loads that have been chrono'ed on othe units.

Factor WW chrono'ed fine out the same gun.

Any ideas?

Could it be al COL issue, the lenght I'm using is from hornady for the specific bullet. However they don't list my powder, IMR lists a speer 200 jhp bullet with 4756 but an COL of 1.17 which seems very short.

According to my calculations (175/150 X 7.8)you will need about 9.1 grains to make a 175 power factor in your set-up. In a .45 case that may be fine for pressure, or maybe not, but it'll probably feel like it has more recoil than necessary. 4756 is really kind of too slow for .45 loads, but works great in Open guns. I'd look at something faster.

[RH45]

I keep 4756 around for when I can't get my hands on VV for my open guns, and every time I get a different batch of 4756, I have to check/adjust my load because it varies so much from batch to batch